1. Field of the Invention
The present invention relates generally to an improved process and apparatus for printing. More specifically, the present invention is directed to a new, novel, process/apparatus for application of a carrier onto paper and attraction of ink to the carrier to form a printed image.
2. Description of the Background
Printing is one of the most important means of mass communication along with television and radio. Printed matter is used in many areas of society including business, recreation, and education. The U.S. printing industry employs over a million people and is among America's fastest growing industries with sales in 1989 of approximately $73 billion.
In most commercial printing, one or more of three basic printing processes are normally involved: (1) offset lithography, (2) relief printing, or (3) gravure printing. Relief printing and gravure printing generally use, respectively, associated raised and sunken printing surfaces. Offset lithography printing normally uses a substantially even printing surface. Of these three processes, offset lithography is the most commonly used printing process. This process may be used to print books, cartons, labels, magazines, stationery, metal containers and many other items.
The operation of modern lithographic printers is based, in general terms, on the principle that oil (grease) and water do not mix. The printing plate typically has image areas to which the printing ink sticks and water is repelled. Correspondingly, the plate also has non-image areas which repel ink and which attract water. The printing plate is normally clamped to a plate cylinder to form a rotary press. As the plate cylinder rotates, the plate is wet by water rollers so the non-image or non-printing areas will repel the printing ink. The plate cylinder then rolls against ink rollers which place the ink on the image or printing areas. The plate cylinder, now containing printers ink on the image areas, typically transfers or offsets this image by rolling against a blanket cylinder which often has a rubber outer coating. A sheet or web of paper may then be fed between the blanket cylinder and an impression cylinder for transferring or offsetting the image onto the paper. The paper is then normally stacked for drying. This process allows for high speed printing. A printing press may print eleven miles worth of paper in an hour and have web speeds of about 300 meters per minute.
Some offset presses, with only a single plate cylinder, print only black or any other single color. Other presses may have four plate cylinders--one each to print red, yellow, blue and black ink. In multi-color printing, the colors of all the plates combine, in a manner well known in the art, to form the tones of the color picture. The black ink roller is generally included to add sharpness to the picture even though, theoretically, the black color may be formed by a combination of the other colors.
Although it is a well established art, the offset printing process has a number of general problems. For instance, this process requires a large number of ink rollers to move the ink in liquid form from an ink fountain to the plate cylinder. A large number of ink rollers is needed in order to maintain an even distribution of color density over the plate cylinder. To complicate matters, pre-mixed ink purchased from manufacturers sometimes has variations in thickness or density and may also have ink pigment variations. The problem of preventing variations in color density as the copies are checked or proofed during a printing job is largely accomplished by making adjustments to the ink flow through the large number of ink rollers. This is a difficult and sometimes stressful job which normally requires trained and experienced personnel. A lengthy, ongoing learning cycle is normally required to become a skillful pressman.
After each color application, roller washing is required and the press must be shutdown during this time. This limits the output or efficiency of the press and thereby results in lower earnings per machine. The use of roller cleaners, which may contain various solvents, shortens the life span of the rollers. These cleaners typically create fumes which may not be healthful to breathe.
The ink drying process, which may take up to 24 hours, may require special paper stacking techniques which will often involve using powders to prevent the sheets from offsetting or smearing into each other. The types of paper, drying additives, and color densities used in the printing job will affect the drying time.
Liquid ink, solvent fumes, drying additives, and spray powder dust are among the chemicals to which printing employees may be regularly exposed. This exposure creates a potential health risk to these employees. As well, disposal of these items can create environmental problems. Such disposal may require governmental permits. The long term trend of environmental legislation and regulation is toward ever-increasing control over emissions. In some cases, B.A.C.T. (Best Available Control Technology) standards must be complied with to obtain a permit for producing emissions. Monetary penalties can be required for non-compliance with environmental regulations. There is also a significant waste, in conventional printing processes, of paper, ink, washing solutions, and time due to these typical problems encountered in operating printing presses.
Consequently a need exists for improvements in printing processes to increase the efficiency of printing presses, decrease operational complexity, reduce the production of waste products, and improve the working environment. Since existing printing presses may be quite expensive and represent a substantial capital expense, any apparatus or process which would alleviate or solve the above enumerated problems should be readily adaptable to conventional printing methods and/or retrofitable to existing printing presses. Of course, any apparatus or process which would solve these problems must also allow for the same high quality and high speed printing that is presently available with conventional printing processes.
Those skilled in the art have long sought and will appreciate the novel features of the present invention which solves these problems.